Commonly used track chains for earthmoving vehicles comprise a plurality of track links. The track links are connected into two parallel endless chains by means of track link hinge joints having track pins joining the ends of adjacent pairs of links and spanning the space between the parallel chains. Drive sprockets drive the track chains and provide locomotion for the vehicle by acting against bushings upon the track pins.
For efficient and low cost operation, it is, of course, desirable to construct a track chain in a manner to provide for long, trouble-free operating life. All track parts are subject to a high rate of wear because of the service they perform and the environment in which they operate. Recent developments in seals and lubrication methods promise to increase the life of some track parts measurably and it appears that the track pin bushing in its present form may well continue to be the first element of the track to fail.
Force for driving the tracks by sprocket is received upon a given portion of the bushing. Additionally, as each such bushing comes into engagement with or tends to be disengaged from the sprocket, there is relative pivotal motion between the two adjacent links. Since the bushing is conventionally secured to one of these links, it is caused to rotate while in engagement with the sprocket. The rotation of the bushing against the sprocket is commonly referred to as "scrubbing" and causes substantial abrasion of the bushing.
Prior art efforts to provide long life bushings have been directed at compensating for such abrasion of the bushings. For example, it has been recommended practice to reverse each bushing after a measured extent of wear, so that such wear occurs on different portions of the bushing surface.
Heretofore, such reversing of the bushing required disassembly and reassembly of the track chain, which is, of course, undesirable due to the high labor cost thereof. Rather, it would clearly be highly desirable to be able to rotate the bushings to present another wear surface thereof to the sprocket with the track chains in place on the vehicle (i.e. not disassembled).